The invention relates to a system for the laser beam deflection for optical measuring systems.
Measuring systems operating by means of laser beams are used in various fields of technology. A special example of such optimal measuring systems are air data systems which detect and analyze the characteristics of the air at a certain distance in precisely defined measuring directions. For example, the speed of the air movement in all three space axes, the air temperature and the air pressure can be measured thereby, Air data systems can be provided, for example, in an airplane or helicopter, a landcraft, a satellite, or stationary on the ground, Such air data systems are particularly used in aviation For example, in an airplane such air data systems are used to detect turbulences and other important air parameters in time, and initiate corresponding controls.
In order to direct the laser beam in different space directions, for example, scanners are used in the known measuring systems, which scanners guide the laser beam along a circular path.
In the journal SPIE, Vol. 2956, February 1997, Page 76, a Doppler LIDAR is described in which the speed components of the air are measured by means of a pulsed laser beam and a scanning mechanism. By means of the scanning mechanism, the beam is guided over various measuring points.
In Applied Optics, Vol. 33, No. 27, Page 6467, 1994, a scanner for an air data measuring system is described in which a rotating mirror deflects a laser beam. By way of stationary mirrors, the deflected beam is guided to the outside through a window of the measuring system in order to detect the measuring data.
In British Patent Document GB 1 238 783, a system for the light beam deflection is described in which an incident light beam is deflected in different directions by a rotating disk.
Finally, International Patent Document WO 99/54082 shows a method for deflecting a laser beam for the machining of material in which a wedge-shaped plate is rotating in order to guide a laser beam impinging in the center in a circular path.
In the case of the known laser beam deflection systems for measuring systems, it is problematic that the pulse repetition frequencies are limited in the upward direction. The known systems are suitable only for continuous-wave lasers or for lasers with low pulse repetition rates because the possible pulse frequency depends from the scanning rate. In addition, a synchronizing or triggering of each laser pulse is required. Moreover, the optical losses are to be kept as low as possible, and simultaneously high power densities should be present.
It is an object of the invention to provide a system and a method for the laser beam deflection for optical measuring systems which are suitable for the operation with extremely high-power lasers, such as pulsed lasers with high power and energy densities as well as high pulse repetition rates, and furthermore have low optical losses.
This object is achieved by means of a system for the laser beam deflection for optical measuring systems and by a method for the laser beam deflection in an optical measuring system. Additional advantageous characteristics, aspects and details of the invention are indicated in the dependent claims, the description and the drawings.
The system according to the invention for the laser beam deflection comprises, for example, an,optical element for the deflection of an incident laser beam and a driving unit for generating a rotational movement between the optical element and the incident laser beam in order to deflect the laser beam in different successive directions, the optical element comprising at least two segments for deflecting the incident laser beam by in each case a fixed deflection angle and, during the rotational movement, the laser beam successively impinging on the at least two segments.
The system according to the invention advantageously comprises a rotatable deflection unit which is connected in the beam direction in front of the optical element and is coupled to the driving element in order to move the laser beam before the impinging on the optical element into a circular path with a parallel beam axis. Accordingly, the rotational movement between the optical element and the impinging laser beam is generated by the rotating movement of the deflection unit. The optical element is preferably constructed to be stationary or fixed.
This has the effect that, during a defined time period, exactly the same deflection angle is always supplied in space and no angular movement takes place during this time. In other words, during the time period in which the laser beam impinges on a segment, the direction of the deflected laser beam is constant in space. When the laser beam impinges on the next segment, a change of direction of the deflected laser beam takes place, the new direction in space again being constant, while the laser beam is deflected by the corresponding segment. This is explained by the fact that, when sweeping over a segment, the laser beam always has the same angle of incidence onto the segment surface. The angle of emergence therefore also remains constant in the case of this segment.
As a result, particularly a high pulse rate can be achieved during the measurement, i.e., pulsed lasers can be used with arbitrarily high pulse repetition rates. Thus, extremely high-power lasers, such as pulsed lasers with high power and energy densities, can be used in optical measuring systems. Furthermore, a very high efficiency is achieved since the optical losses by means of the system according to the invention are extremely low. Additionally, a very high accuracy and stability of direction of the deflected laser beam, as well as a considerable temperature independence, is obtained. The system according to the invention can therefore have a very sturdy construction with respect to vibrations, shocks and accelerations. In addition, the system according to the invention is very compact with a low volume, which is particularly advantageous for applications in aviation and space travel.
The system according to the invention can be implemented almost without wear or with a long service life of the bearings, and consists of only a few components, making it particularly cost-effective.
Furthermore, by means of only one laser, several measuring positions, whose number is, for example, between 2 and approximately 100, can be detected almost isochronously. In this case, the scanning frequency of the individual measuring positions can be several hundred hertz. Idle times, during which the unit is interrupted because of switching operations, are avoided.
The optical element is advantageously arranged such that the incident laser beam carries out a circular path during the rotational movement on the surface of the optical element.
The optical element preferably has a disk-shaped or ring-shaped design, and the individual segments of the optical element preferably have a wedge-shaped construction, the wedge angle of each segment defining its deflection angle.
The segments of the optical element advantageously have surfaces which are inclined with respect to the beam axis of the incident laser beam, the angles of inclination of the surface of each segment together with the refractive index of the optical material defining its deflection angle. In particular, during the impinging of the laser beam onto a segment, the deflected laser beam maintains a constant direction in space.
Preferably, the segments are designed such that the incident laser beam is deflected toward the axis of rotation or the axis of symmetry. As a result, the window from which the laser beam emerges in the case of a corresponding optical measuring system, can be kept particularly small. However, it is also conceivable that the segments deflect the incident laser beam away from the axis of rotation.
For example, the segments are designed such that the respective incident laser is deflected into a different defined direction by each segment. However, several segments may also have identical designs in order to, during the rotational movement, deflect the laser beam several times into one and the same defined direction.
A transition area advantageously exists between the two adjoining segments, The transition are permits a change of direction of the laser beam without any beam interruption. As a result, a fading-over from one measuring point or one measuring direction to another measuring point or another measuring direction can take place during the measuring.
It is particularly advantageous for the optical element to have a spherical or aspherical construction on one side, for example, on the rear side, or to have a spherically or aspherically constructed surface element with a positive focal length. As a result, a displacement of the laser beam incident on the optical element during the circular-path movement of the laser beam at a desired measuring point can be corrected, so that the measuring position can be maintained particularly precisely.
The optical element is preferably flattened or constructed as a plane surface in a partial area which is not utilized for the beam deflection, or it has a recess in the partial area. As a result, a further weight reduction and miniaturization of the system can be achieved.
The optical element is preferably transparent, the respective deflection angle being generated by optical refraction in segments. However, it is also conceivable to develop the optical element in a reflecting manner, the respective deflection angle being generated by reflection on the segments or segment surfaces.
The dwell time of the deflected laser beam in a defined space direction can be determined as a function of the angular range of the respective segment and of the rotation frequency. This results in a particularly high flexibility with respect to the manner of measuring.
The segments preferably have a spherical or aspherical surface on one side. As a result a correction of a parallel beam displacement can be achieved.
The segments are preferably designed such that the beam deflection takes place toward the axis of rotation. The outlet hole for the laser beam can therefore be kept particularly small.
Advantageously, the optical element according to the invention is provided or can be used in a system for the laser beam deflection according to the invention. Advantages and characteristics of the optical element according to the invention also apply to the laser beam deflection system according to the invention.
According to another aspect of the invention, a method is disclosed for the laser beam deflection, by which an incident laser beam is successively deflected in at least two different directions by an optical element, in which case a deflecting unit rotates which is connected in front, and the laser beam impinging in a displaced manner with respect to the axis of rotation during a rotation in each case for a time period t impinges on at least two segments of the optical element, and each segment deflects the laser beam during the time period t into exactly one defined direction.
By means of the method according to the invention, particularly extremely high-power lasers or pulsed lasers with arbitrarily high pulse repetition rates can be used in optical measuring systems, and the scanning frequency of the individual measuring positions can, for example, amount to several hundred hertz. In addition, the advantages and characteristics which are indicated with respect to the system according to the invention and to the optical element according to the invention also apply to the method according to the invention.
Advantageously, the method is implemented by means of a system according to the invention.
In the following, the invention will be described as an example by means of the figures.